Chainsaw Repair

Bars come from the factory as .050", .058", or 063" gauge. To change this you have to buy another bar.

I know and understand what you are saying.
The bar is definitely a .050 gauge.
The chain is definitely a .050 gauge chain and moves easily in my other .050 gauge bars.
But it no longer spins freely in the .050 bar that I just took off the 371xp.
The same bar, the same chain that was used yesterday when the oiling problem was noticed.
The gauge of the bar seems to have significantly decreased due to the over heating of the chain/bar.
The tip is fine, spins good/easy with chain, but the channel in the bar is no longer .050.

Find where it is tight and open it up

Thanks, but I ordered the bearing first thing this morning.

Although all of my oiler parts look to be in good condition,
I got replacement drive wheel, the oiler piston and a new washer that goes under the drive wheel, that was missing.

Other than the missing washer, I really could not find a problem with the whole oiler system.
So it got cleaned up and put back together with the new parts.
Just need the new drum bearing to get things all put back together.
You ask "what happened to the old bearing?"
It disappeared.  Probably got thrown out with a bunch of paper towels while cleaning up.
Par for me.  Try to fix one thing and break or loose another thing. 
I could never make a living as a mechanic.